SOLR-2020: Maven configuration: * Switched the scope from runtime to compile for the two httpcomponents dependencies in the solrj POM - compilation fails unless these are on the classpath. * Removed commons-httpclient dependency from the solr-core POM. It gets this dependency transitively through solrj. * Added the two httpcomponents dependencies with test scope to the POM for solr-core (under which all Solr tests are run in the Maven build, including those of solrj); otherwise tests fail, because these are optional dependencies of solrj, and are not transitively included on the test classpath. * Added a httpcomponents.version property to the Lucene/Solr grandparent POM, and used it in the <dependencyManagement> declarations for the two httpcomponents dependencies.